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Sprinting pollen prepared for quick start
Many of us are interested in sporting records but it is not only sport that provides records of note. The natural world also has its share of record holders that are every bit as fascinating as their human counterparts. Thus, Stone et al. (Murdoch University and University of Western Australia; pp. 369-378) comment that pollen tube elongation rates vary enormously between species; Zea mays exhibiting one of the fastest previously recorded in vivo rates (2.7 micrometres s-1, reducing to 1.14 micrometres s-1 in vitro). However, maize pollen is positively sluggish compared with that of Conospermum species (family Proteaceae). The authors have studied the germination in vitro of Conospermum pollen, revealing the unusual (but not unique) feature of the emergence of not one but up to three pollen tubes. The emergence of multiple tubes also occurs in pollen germinating in vivo. The two pollen nuclei travel in one of the tubes but the ‘empty’ tubes also continue to grow. And it is the extension rate of the tubes that is particularly remarkable. The rate recorded during the first few seconds after emergence in vitro is extraordinarily high: some tubes achieve 55 micrometres s-1! The authors suggest that this early growth is much too fast to be dependent on concurrent biosynthesis of cell wall components and conclude that ready-made stock must be available to enable this ‘quick get-away’. After the rapid start, the rate of extension then declines to about 2 micrometres s-1. This overall rate (which is still fast for in vitro conditions) is achieved by a series of very short growth spurts (several per second) as revealed by video microscopy. What controls the bursts is not known, but the authors showed that they were not affected by calcium channel blockers. So, even though the system is not fully understood, we can only be truly amazed by the extraordinary growth rates of these pollen tubes.
Professor J. A. BryantUniversity of Exeter, UK
j.a.bryant{at}exeter.ac.uk
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